Acoustic resonator and method for fabricating the same

ABSTRACT

An acoustic resonator includes a membrane layer disposed on an insulating layer; a cavity formed by the insulating layer and the membrane layer; a resonating portion disposed on the cavity and having a first electrode, a piezoelectric layer, and a second electrode stacked thereon; a protective layer disposed on the resonating portion; and a hydrophobic layer formed on the protective layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 USC 119(a) of Korean PatentApplication No. 10-2017-0066487 filed on May 30, 2017, in the KoreanIntellectual Property Office, the entire disclosure of which isincorporated herein by reference for all purposes, and Korean PatentApplication No. 10-2017-0103830 filed on Aug. 16, 2017, in the KoreanIntellectual Property Office, the entire disclosure of which isincorporated herein by reference for all purposes.

BACKGROUND 1. Field

This application relates to an acoustic resonator and a method formanufacturing the same.

2. Description of the Background

In accordance with a rapid development of mobile communications devices,chemical and biological testing devices, and the like, demand forcompact and lightweight filters, oscillators, resonant elements,acoustic resonant mass sensors, and the like, has recently increased.

As a means of implementing such compact and lightweight filters,oscillators, resonant elements, acoustic resonant mass sensors, and thelike, a film bulk acoustic resonator (FBAR) may be utilized.

FBARs may be mass produced at low cost and FBARs may be subminiaturized.Further, FBARs may provide a high quality factor Q value, a mainproperty of a filter, may be used even in a micro-frequency band, andmay particularly allow for use with personal communications system (PCS)and digital cordless system (DCS) bands.

In general, the FBAR has a structure including a resonating portionimplemented by a first electrode, a piezoelectric layer, and a secondelectrode stacked in sequence on a substrate.

An operational principle of the FBAR includes inducing an electric fieldin the piezoelectric layer by applying electric energy to the first andsecond electrodes. The electric field causes a piezoelectric phenomenonof the piezoelectric layer, thereby causing the resonating portion tovibrate in a predetermined direction. As a result, a bulk acoustic waveis generated in the same direction as the vibration direction of theresonating portion, thereby causing resonance.

That is, the FBAR, an element using bulk acoustic waves (BAWs), mayimprove frequency characteristics of a BAW element and may also beimplemented in a wideband, as an effective electromechanical couplingcoefficient (kt²) of the piezoelectric layer is increased.

The above information disclosed in this Background section is only forenhancement of understanding of the background of the disclosure andtherefore it may contain information that does not form any part of theprior art nor what the prior art may suggest to a person of ordinaryskill in the art.

SUMMARY

This summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used as an aid in determining the scope of the claimed subjectmatter.

In one general aspect, an acoustic resonator includes a membrane layerdisposed on an insulating layer, a cavity formed by the insulating layerand the membrane layer, a resonating portion disposed on the cavity andhaving a first electrode, a piezoelectric layer, and a second electrodestacked thereon, a protective layer disposed on the resonating portion;and a hydrophobic layer disposed on the protective layer.

The hydrophobic layer may be further disposed on an upper surface of thecavity. The hydrophobic layer may be further disposed on at least aportion of a lower surface and a side surface of the cavity. Thehydrophobic layer may be a self-assembled monolayer. The hydrophobiclayer may include a fluorine (F) component. The hydrophobic layer mayfurther include a silicon (Si) component.

The resonating portion may include a center portion, and an extendingportion extending outward from the center portion and in which aninsertion layer is disposed below the piezoelectric layer. Thepiezoelectric layer may include a piezoelectric portion disposed in thecenter portion, and a bending portion disposed in the extending portionand extending inclined from the piezoelectric portion along an inclinedsurface of the insertion layer.

In another general aspect, a method for manufacturing an acousticresonator includes disposing a sacrificial layer on an insulating layerand forming a pattern penetrating through the sacrificial layer;disposing a membrane layer on the sacrificial layer; stacking a firstelectrode, a piezoelectric layer, and a second electrode on the membranelayer to form a resonating portion; removing a portion of thesacrificial layer to form a cavity; disposing a protective layer on theresonating portion; and disposing a hydrophobic layer on the protectivelayer.

Disposing the hydrophobic layer may include disposing a fluorocarbonfunctional group on the protective layer. Disposing the hydrophobiclayer may include surface-treating the protective layer using aprecursor having a silicon head before forming the hydrophobic layer.

The method for manufacturing an acoustic resonator may further includedisposing the hydrophobic layer on an upper surface of the cavity. Themethod may further include disposing the hydrophobic layer on at least aportion of a lower surface and a side surface of the cavity.

The hydrophobic layer may be a self-assembled monolayer.

The method may further include trimming before disposing the hydrophobiclayer.

Forming the resonating portion may include forming a first electrode onthe membrane layer, forming a piezoelectric layer including apiezoelectric portion stacked on the first electrode layer and a bendingportion extending inclined from a boundary of the piezoelectric portion,and forming a second electrode on the piezoelectric layer.

The method for manufacturing an acoustic resonator may further include,before disposing the piezoelectric layer, disposing an insertion layerbelow the bending portion, and the bending portion may have an inclinedsurface along an inclined surface of the insertion layer.

In another general aspect, an acoustic resonator includes a membranelayer disposed on an insulating layer, a cavity formed by the insulatinglayer and the membrane layer, and a resonating portion disposed on thecavity including a first electrode, a piezoelectric layer comprising aninclined portion disposed on the first electrode, and a second electrodedisposed on the piezoelectric layer. The second electrode comprises anend portion extending partway along the inclined portion.

The acoustic resonator may further include a protective layer disposedon the resonating portion. The acoustic resonator may further include ahydrophobic layer disposed on the protective layer.

The inclined portion has a length I_(s) and the end portion extendsalong the inclined portion a distance W_(e), and W_(e)/I_(s) may begreater than 0.2 and less than 0.9.

Other features and aspects will be apparent from the following detaileddescription, the drawings, and the claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a plan view of a first example of an acoustic resonator.

FIG. 2 is a cross-sectional view taken along a line I-I′ of FIG. 1.

FIG. 3 is a cross-sectional view taken along a line II-II′ of FIG. 1.

FIG. 4 is a cross-sectional view taken along a line III-III′ of FIG. 1.

FIGS. 5, 6, 7, and 8 are cross-sectional views illustrating an examplemethod for manufacturing an example acoustic resonator.

FIGS. 9 and 10 are cross-sectional views schematically illustrating asecond example of an acoustic resonator.

FIG. 11 is a graph illustrating resonance attenuation of the acousticresonator according to a second electrode structure of the acousticresonator.

FIGS. 12A and 12B schematically illustrate example molecular structuresof precursors used as an adhesion layer of a hydrophobic layer.

FIG. 13 schematically illustrates an example of a molecular structure ofthe hydrophobic layer.

FIGS. 14 and 15 are schematic circuit diagrams of example filters.

FIG. 16 illustrates a hydroxy group adsorbed onto a protective layer onwhich the hydrophobic layer is not formed.

FIG. 17 schematically illustrates a process of forming a hydrophobiclayer on a protective layer in an example method for manufacturing anexample acoustic resonator.

FIG. 18 is a graph illustrating a change in a frequency according tohumidity and time for an acoustic resonator (Exemplary Example) in whichthe hydrophobic layer is formed on the protective layer and an acousticresonator (Comparative Example) in which the hydrophobic layer is notformed on the protective layer.

FIG. 19 illustrates the hydrophobic layer formed on the protectivelayer.

Throughout the drawings and the detailed description, the same referencenumerals refer to the same elements. The drawings may not be to scale,and the relative size, proportions, and depiction of elements in thedrawings may be exaggerated for clarity, illustration, and convenience.

DETAILED DESCRIPTION

The following detailed description is provided to assist the reader ingaining a comprehensive understanding of the methods, apparatuses,and/or systems described herein. However, various changes,modifications, and equivalents of the methods, apparatuses, and/orsystems described herein will be apparent after an understanding of thedisclosure of this application. For example, the sequences of operationsdescribed herein are merely examples, and are not limited to those setforth herein, but may be changed as will be apparent after anunderstanding of the disclosure of this application, with the exceptionof operations necessarily occurring in a certain order. Also,descriptions of features that are known in the art may be omitted forincreased clarity and conciseness.

The features described herein may be embodied in different forms, andare not to be construed as being limited to the examples describedherein. Rather, the examples described herein have been provided merelyto illustrate some of the many possible ways of implementing themethods, apparatuses, and/or systems described herein that will beapparent after an understanding of the disclosure of this application.

An aspect of the present disclosure may provide a solution for a problemthat frequency fluctuation is increased or performance of a resonator isdegraded due to a hydroxy group (OH group) adsorbed onto a protectivelayer of an acoustic resonator when the acoustic resonator is used in ahumid environment or left at room temperature for a long time.

Acoustic Resonator

FIG. 1 is a plan view of a first example of an acoustic resonatoraccording to an exemplary embodiment in the present disclosure and FIG.2 is a cross-sectional view taken along a line I-I′ of FIG. 1. Further,FIG. 3 is a cross-sectional view taken along a line II-II′ of FIG. 1 andFIG. 4 is a cross-sectional view taken along a line III-III′ of FIG. 1.

Referring to FIGS. 1 through 4, the first example of an acousticresonator 100 is a film bulk acoustic resonator (FBAR) and includes asubstrate 110, an insulating layer 115, a membrane layer 150, a cavityC, a resonating portion 120, a protective layer 127, and a hydrophobiclayer 130.

The substrate 110 may be a silicon substrate. For example, as thesubstrate 110, a silicon wafer may be used, or a silicon on insulator(SOI) type of substrate may be used.

The insulating layer 115 formed on the substrate 110 electricallyisolates the substrate 110 and the resonating portion 120 from eachother. Further, the insulating layer 115 prevents the substrate 110 frombeing etched by etching gas, when forming the cavity C in a process ofmanufacturing of the acoustic resonator.

In this case, the insulating layer 115 may be formed of at least one ofsilicon dioxide (SiO₂), silicon nitride (Si₃N₄), aluminum oxide (Al₂O₂),and aluminum nitride (AlN) and may be formed on the substrate 110 by anyone of chemical vapor deposition, RF magnetron sputtering, andevaporation.

A sacrificial layer 140 is formed on the insulating layer 115, and thecavity C and an etching stop part 145 is disposed in the sacrificiallayer 140.

The cavity C may be formed as air and may be formed by removing aportion of the sacrificial layer 140.

As the cavity C is formed in the sacrificial layer 140, the resonatingportion 120 formed on the sacrificial layer 140 is substantially flat.

The etching stop part 145 may be disposed along a boundary of the cavityC. The etching stop part 140 may be provided to prevent the cavity Cfrom being etched beyond a cavity region in the process of forming thecavity C. Therefore, a horizontal area of the cavity C may be defined bythe etching stop part 145 and a vertical area of the cavity C may bedefined by a thickness of the sacrificial layer 140.

The membrane layer 150 is disposed on the sacrificial layer 140 anddefines a thickness (or a height as viewed in FIGS. 2 through 4) of thecavity C together with the insulating layer 115. Therefore, the membranelayer 150 includes a material which is not easily removed in a processof forming the cavity C.

For example, in a case in which halide-based etching gases such asfluorine (F), chlorine (Cl), and the like are used to remove a portion(for example, a cavity region) of the sacrificial layer 140, themembrane layer 150 may be formed of a material having low reactivitywith these etching gases. In this case, the membrane layer 150 mayinclude at least one of silicon dioxide (SiO₂) and silicon nitride(Si₃N₄).

Further, the membrane layer 150 may include a dielectric layercontaining at least one material of magnesium oxide (MgO), zirconiumoxide (ZrO₂), aluminum nitride (AlN), lead zirconate titanate (PZT),gallium arsenide (GaAs), hafnium oxide (HfO₂), aluminum oxide (Al₂O₃),titanium oxide (TiO₂), and zinc oxide (ZnO), or may be formed of a metallayer containing at least one material of aluminum (Al), nickel (Ni),chromium (Cr), platinum (Pt), gallium (Ga), and hafnium (Hf). However,the configuration of the present disclosure is not limited thereto.

A seed layer (not shown) formed of aluminum nitride (AlN) may be formedon the membrane layer 150. Specifically, the seed layer may be disposedbetween the membrane layer 150 and a first electrode 121. The seed layermay be formed of a dielectric or a metal having a hexagonal-close-packed(HCP) structure other than AlN. In a case in which the seed layer isformed of the metal, the seed layer may be formed of, for example,titanium (Ti).

The resonating portion 120 includes a first electrode 121, apiezoelectric layer 123, and a second electrode 125. The resonatingportion 120 may be formed by stacking the first electrode 121, thepiezoelectric layer 123, and the second electrode 125 in sequence frombelow. Therefore, in the resonating portion 120, the piezoelectric layer123 may be disposed between the first electrode 121 and the secondelectrode 125.

Since the resonating portion 120 is formed on the membrane layer 150,the resonating portion 120 may be formed by stacking the membrane layer150, the first electrode 121, the piezoelectric layer 123, and thesecond electrode 125 in sequence on the substrate 110.

The resonating portion 120 allows the piezoelectric layer 123 toresonate in response to first signals applied to the first electrode 121and the second electrode 125 to generate a resonance frequency and toanti-resonate in response to second signals applied to the firstelectrode 121 and he second electrode 125 to generate an anti-resonancefrequency.

In a case in which an insertion layer 170, to be described below, isformed, the resonating portion 120 may be classified into a centerportion S on which the first electrode 121, the piezoelectric layer 123,and the second electrode 125 are stacked to be substantially flat, andan extending portion E, in which the insertion layer 170 is interposedbetween the first electrode 121 and the piezoelectric layer 123.

The center portion S is a region disposed at a center of the resonatingportion 120 and the extending portion E is a region disposed along aperimeter of the center portion S. Therefore, the extending portion Erefers to a region extending outwardly from the center portion S.

The insertion layer 170 includes an inclined surface L by whichthickness of the insertion layer is increased as a distance from thecenter portion S is increased.

In the extending portion E, the piezoelectric layer 123 and the secondelectrode 125 are disposed on the insertion layer 170. Therefore, thepiezoelectric layer 123 and the second electrode 125 disposed in theextending portion E include inclined surfaces along the inclined surfaceL of the insertion layer 170. The inclined surface L forms an edge ofthe insertion layer 170 extending toward the center portion S.

The extending portion E is included in the resonating portion 120, andresonance may also occur in the extending portion E, accordingly.However, the occurrence of resonance is not limited thereto, andresonance may not occur in the extending portion E depending on astructure of the extending portion E, and hence, may occur in only thecenter portion S.

The first electrode 121 and the second electrode 125 may be formed of anelectrical conductor, and may be formed of, for example, gold,molybdenum, ruthenium, iridium, aluminum, platinum, titanium, tungsten,palladium, tantalum, chromium, nickel, or a metal including at least onethereof, but are not limited thereto.

The first electrode 121 may have a wider area than the second electrode125 and a first metal layer 180 may be disposed on the first electrode121 along an outer portion of the first electrode 121. Therefore, thefirst metal layer 180 may be disposed to surround the second electrode125.

Since the first electrode 121 is disposed on the membrane layer 150, itmay be generally flat. On the other hand, since the second electrode 125may be disposed on the piezoelectric layer 123, the second electrode 125may have a bending formed to correspond to a shape of the piezoelectriclayer 123.

The second electrode 125 may be entirely disposed in the center portionS and may be partially disposed in the extending portion E. Accordingly,the second electrode 125 may be classified into a portion disposed on apiezoelectric portion 123 a of the piezoelectric layer 123 and a bendingportion 123 b of the piezoelectric layer 123 which are described in moredetail below.

For example, the second electrode 125 may be disposed to cover theentirety of the piezoelectric portion 123 a and a portion of an inclinedportion 1231 of the bending portion 123 b of the piezoelectric layer123. Therefore, a portion of the second electrode 125 a disposed in theextending portion E may have a smaller area than an inclined surface ofthe inclined portion 1231, and the second electrode 125 in theresonating portion 120 may have a smaller area than the piezoelectriclayer 123.

The piezoelectric layer 123 may be formed on the first electrode 121. Ina case in which the insertion layer 170, to be described below, isformed, the piezoelectric layer 123 may be formed on the first electrode121 and the insertion layer 170.

The material of the piezoelectric layer 123 includes, for example, zincoxide (ZnO), aluminum nitride (AlN), doped aluminum nitride, leadzirconate titanate, quartz, and the like. For example, the dopedaluminum nitride may further include a rare earth metal or a transitionmetal. As an example, the rare earth metal may include at least one ofscandium (Sc), erbium (Er), yttrium (Y), cerium (Ce), and lanthanum(La). The transition metal may include at least one of hafnium (Hf),titanium (Ti), zirconium (Zr), tantalum (Ta), niobium (Nb), andmagnesium (Mg).

The piezoelectric layer 123 may include a piezoelectric portion 123 adisposed on the center portion S and a bending portion 123 b disposed onthe extending portion E.

The piezoelectric portion 123 a is a portion which is directly disposedon a top surface of the first electrode 121. Therefore, thepiezoelectric portion 123 a is interposed between the first electrode121 and the second electrode 125 to form a flat structure together withthe first electrode 121 and the second electrode 125.

The bending portion 123 b is a region which is extended outwardly fromthe piezoelectric portion 123 a and disposed in the extending portion E.

The bending portion 123 b is disposed on the insertion layer 170, to bedescribed below, and is formed to be uplifted along an edge of theinsertion layer 170. Accordingly, the piezoelectric layer 123 may bebent at a boundary between the piezoelectric portion 123 a and thebending portion 123 b, and the bending portion 123 b may be uplifted tocorrespond to a thickness and an edge of the insertion layer 170.

The bending portion 123 b may be classified into an inclined portion1231 and a spreading portion 1232.

The inclined portion 1231 refers to a portion formed to be inclinedalong the inclined surface L of the insertion layer 170, to be furtherdescribed below. In addition, the spreading portion 1232 refers to aportion which is extended outwardly from the inclined portion 1231.

The inclined portion 1231 is parallel to the inclined surface L of theinsertion layer 170, and an inclined angle of the inclined portion 1231may be the same as an inclined angle (θ in FIG. 4) of the inclinedsurface L of the insertion layer 170.

The insertion layer 170 is disposed along a surface formed by themembrane layer 150, the first electrode 121, and the etching stop part145.

The insertion layer 170 may be disposed around the center portion S tosupport the bending portion 123 b of the piezoelectric layer 123.Therefore, the bending portion 123 b of the piezoelectric layer 123 maybe classified into the inclined portion 1231 and the spreading portion1232 depending on the shape of the insertion layer 170.

The insertion layer 170 may be disposed on a region other than thecenter portion S. For example, the insertion layer 170 may be disposedon the entire region other than the center portion S or a partial regionother than the center portion S.

Further, at least a portion of the insertion layer 170 may be disposedbetween the piezoelectric layer 123 and the first electrode 121.

The insertion layer 170 disposed along a boundary of the center portionS has a side surface where a thickness of the insertion layer 170 isincreased as a distance from the center portion S is increased. Thereby,the side surface of the insertion layer 170 disposed to be adjacent tothe center portion S is an inclined surface L having a constant inclinedangle θ.

In a case in which the inclined angle θ of the side surface L of theinsertion layer 170 is less than 5°, in order to manufacture theinsertion layer 170, since the thickness of the insertion layer 170needs to be extremely thin or an area of the inclined surface L needs tobe extremely large, it is difficult to substantially implement theinsertion layer 170.

Further, in a case in which the inclined angle θ of the side surface ofthe insertion layer 170 is greater than 70°, the inclined angle θ of theinclined portion 1231 of the piezoelectric layer 123 stacked on theinsertion layer 170 may also be greater than 70°. In this case, sincethe piezoelectric layer 123 is excessively bent, a crack may occur froma bent portion of the piezoelectric layer 123.

Therefore, the inclined angle θ of the inclined surface L may have therange of greater than or equal to 5° and less than or equal to 70°.

The insertion layer 170 may include a dielectric material such assilicon dioxide (SiO₂), aluminum nitride (AlN), aluminum oxide (Al₂O₃),silicon nitride (Si₃N₄), magnesium oxide (MgO), zirconium oxide (ZrO₂),lead zirconate titanate (PZT), gallium arsenide (GaAs), hafnium oxide(HfO₂), aluminum oxide (Al₂O₃), titanium oxide (TiO₂), zinc oxide (ZnO),or the like, but may be formed of a material different from thepiezoelectric layer 123. Further, a region including the insertion layer170 may also be formed as air, as needed. This air may be implemented byforming the entirety of the resonating portion 120 and then removing theinsertion layer 170 in the manufacturing process to leave a space in theshape of the illustrated insertion layer 170 bounded below by the firstelectrode 121 and bounded above by the inclined portion 1231 andspreading portion 1232 of the bending portion 123 b of the piezoelectriclayer 123.

According to the first example, the thickness of the insertion layer 170may be the same as or similar to the thickness of the first electrode121. Further, the insertion layer 170 thickness may be similar to orless than the piezoelectric layer 123 thickness. For example, theinsertion layer 170 may have a thickness of 100 Å or more, but may bethinner than the thickness of the piezoelectric layer 123. However, theconfiguration of the present example is not limited thereto.

The resonating portion 120 according to the present example configuredas described above may be spaced apart from the substrate 110 throughthe cavity C formed as air.

The cavity C may be formed by supplying an etching gas (or etchingsolution) into an injection hole H (FIGS. 1 and 3) to remove a portionof the sacrificial layer 140 in the process of manufacturing theacoustic resonator.

The protective layer 127 may be disposed along a surface of the acousticresonator 100 and may protect the acoustic resonator 100 from theoutside. The protective layer 127 may be disposed along a surface formedby the second electrode 125, the bending portion 123 b of thepiezoelectric layer 123, and the insertion layer 170.

The protective layer 127 may be formed of an insulating materialincluding any of silicon oxide based insulating material, siliconnitride based insulating material, aluminum oxide based insulatingmaterial, and aluminum nitride based insulating material, but is notlimited thereto.

The first electrode 121 and the second electrode 125 may be extendedexternally from the resonating portion 120, and a first metal layer 180and a second metal layer 190 are disposed on upper surfaces of theexternally extended portions of the first electrode 121 and the secondelectrode 125, respectively.

The first metal layer 180 and the second metal layer 190 may be formedof metal materials such as gold (Au), a gold-tin (Au—Sn) alloy, copper(Cu), a copper-tin (Cu—Sn) alloy, and the like.

The first metal layer 180 and the second metal layer 190 may serve asconnection wirings that electrically connect the electrodes 121 and 125of the acoustic resonator with electrodes of another acoustic resonatordisposed to be adjacent to the acoustic resonator, or may serve asexternal connection terminals. However, the first metal layer 180 andthe second metal layer 190 are not limited thereto.

Although FIG. 2 illustrates a case in which the insertion layer 170 isdisposed below the second metal layer 190, the configuration of thepresent disclosure is not limited thereto, but a structure in which theinsertion layer 170 is removed below the second metal layer 190 may alsobe implemented as needed. For example, FIGS. 9 and 10 show a secondexample of an acoustic resonator including the insertion layer 170removed below the first metal layer 180 and the second metal layer 190.

The first metal layer 180 may penetrate through the insertion layer 170and the protective layer 127 and be coupled to the first electrode 121.

Further, as illustrated in FIG. 3, the first electrode 121 may have awider area than the second electrode 125, and the first metal layer 180may be formed around the first electrode 121.

Therefore, the first metal layer 180 may be disposed along a perimeterof the resonating portion 120 and disposed to surround the secondelectrode 125 accordingly. However, the first metal layer 180 is notlimited thereto.

As described above, the second electrode 125 is disposed on thepiezoelectric portion 123 a and the inclined portion 1231 of thepiezoelectric layer 123. In addition, a portion 125 a (FIG. 4) of thesecond electrode 125 disposed on the inclined portion 1231 of thepiezoelectric layer 123, that is, the portion of second electrode 125 adisposed on the extending portion E may be disposed on only a portion ofthe inclined surface of the inclined portion 1231 of the piezoelectriclayer 123, not the entirety of the inclined surface of the inclinedportion 1231.

FIG. 11 is a graph illustrating resonance attenuation of the acousticresonator according to the second electrode 125 structure of the exampleacoustic resonator 100.

FIG. 11 is a graph obtained by measuring attenuation of an acousticresonator while changing a size of the portion of second electrode 125 adisposed in the extending portion E, in the acoustic resonator 100 inwhich the thickness of the insertion layer 170 is 3000 Å, the inclinedangle θ of the inclined surface L of the insertion layer 170 is 20°, alength of the inclined surface L is 0.87 μm, which is the first exampleof an acoustic resonator 100 illustrated in FIGS. 2 and 3. Table 1 belowsummarizes values of the graph illustrated in FIG. 11.

TABLE 1 Length (μm) of Portion of Second Electrode Length (μm) ofPortion in Extending Portion of Second Electrode W_(e)/Length (μm) ofInclined in Extending Portion Attenuation(dB) Portion 1231 Surface I_(s)0.2 36.201 0.23 0.4 37.969 0.46 0.5 38.868 0.575 0.6 38.497 0.69 0.836.64 0.92 1 35.33 1.149 ※ length of inclined surface L = 0.87 μm

Since the inclined surface of the piezoelectric layer 123 is formed inthe same shape along the inclined surface L of the insertion layer 170,the length I_(s) of the inclined surface of the piezoelectric layer 123is the same as the length of the inclined surface L of the insertionlayer.

Referring to FIG. 11 and Table 1, in the acoustic resonator in which thelength I_(s) of the inclined surface of the inclined portion 1231 of thepiezoelectric layer 123 in the extending portion E is 0.87 μm, it wasmeasured that attenuation was lowest when the length of the portion ofthe second electrode 125 a, W_(e) was 0.5 μm. In addition, in a case inwhich the length of the portion of the second electrode 125 a in theextending portion E is greater than or less than this length, it isshown that attenuation is increased and resonance attenuation isdegraded.

Also, when considering a ratio (W_(e)/I_(s)) of the length (W_(e)) ofthe portion of the second electrode 125 a to the length (I_(s)) of theinclined surface of the inclined portion 1231 of the piezoelectric layer123 in the extending portion E, it can be seen that attenuation ismaintained over 37 dB in a case in which the ratio (W_(e)/I_(s)) is 0.46to 0.69 as illustrated in FIG. 11 and presented in Table 1.

Therefore, in order to secure resonance attenuation, the acousticresonator 100 according to the first example, may limit the ratio(W_(e)/I_(s)) of the maximum length (W_(e)) of the portion of the secondelectrode 125 a and the length (I_(s)) of the inclined surface of theinclined portion 1231 in the extending portion E to the range of 0.46 to0.69. However, the entire configuration of the present disclosure is notlimited to the above-mentioned range, and the above-mentioned range maybe changed depending on a size of the inclined angle θ or a change inthe thickness of the insertion layer 170, and may also be changed as aresonance frequency of the resonator is changed.

In a case in which the acoustic resonator is used in a humid environmentor left at room temperature for a long time, a problem that frequencyfluctuation is increased or performance of the resonator is degraded hasoccurred by mass loading caused by a hydroxy group (OH group) adsorbedonto the protective layer of the acoustic resonator.

FIG. 16 illustrates a hydroxy group adsorbed onto a protective layer onwhich the hydrophobic layer is not formed and FIG. 19 illustrates thehydrophobic layer formed on the protective layer.

Referring to FIG. 16, in a case in which the hydrophobic layer is notformed, when an acoustic resonator is used in a humid environment orleft at room temperature for a long time, hydroxylate may be formed dueto the hydroxy group (OH group) adsorbed onto the protective layer.Since the hydroxylate has high and unstable surface energy, it attemptsto decrease the surface energy by adsorbing water or the like, therebyresulting in the mass loading.

On the other hand, referring to FIG. 19, in a case in which thehydrophobic layer 130 is formed on the protective layer 127, since thesurface energy is low and stable, the hydroxylate does not need todecrease the surface energy by adsorbing water and the hydroxyl group(OH group). Therefore, the hydrophobic layer 130 may serve to preventthe water and the hydroxy group (OH group) from being adsorbed, therebysignificantly reducing frequency fluctuation and uniformly maintainingperformance of the resonator.

FIG. 18 is a graph illustrating a change in a frequency according tohumidity and time for an exemplary example of the acoustic resonator inwhich the hydrophobic layer is formed on the protective layer and acomparative example of an acoustic resonator in which the hydrophobiclayer is not formed on the protective layer. In an experiment method,the exemplary example and the comparative example are placed in amoisture absorption chamber and a change in frequency was measured whilechanging humidity as illustrated in FIG. 18.

to the experimental results shown in FIG. 18, confirm that the acousticresonator in which the hydrophobic layer is formed on the protectivelayer has much less frequency variation according to a change inhumidity and time. Further, the exemplary example has a frequencyvariation at the time of ending of the experiment which is less than thefrequency variation at the time of starting of the experiment.

In an example, to improve adhesion between the hydrophobic layer 130 andthe protective layer 127, a precursor is used. Referring to FIGS. 12Aand 12B, the precursor may be a hydrocarbon having a silicon head, or asiloxane having a silicon head.

Referring to FIG. 13, the hydrophobic layer 130 may be a fluorocarbonsuch as perfluorodecyltrichlorosilane, but is not limited thereto, andmay be formed of a material having a contact angle of 90° or more bywater after deposition. For example, the hydrophobic layer 130 includesa fluorine (F) component, and for example, the hydrophobic layerincludes fluorine (F) and silicon (Si). For example, the hydrophobiclayer 130 may be heptadecafluorodecyltrimethoxysilane,(heptafluoroisopropoxy)propyltrichlorosilane,octadecyldimethylchlorosilane, octadecyltrichlorosilane,tris(trimethylsiloxy)-silylethyldimethylchlorosilane,octyldimethylchlorosilane, dimethyldichlorosilane,butyldimethylchlorosilane, or trimethylchlorosilane.

The hydrophobic layer 130 may be formed of a self-assembled monolayer(SAM) 131, not a polymer. In a case in which the hydrophobic layer 130is formed of a polymer, mass due to the polymer may affect theresonating portion 120. However, since the first example of the acousticresonator 100 has the hydrophobic layer 130 formed of the self-assembledmonolayer 131, the change in the frequency of the acoustic resonator 100may be significantly reduced.

Further, in a case in which the hydrophobic layer 130 is formed of apolymer, when the hydrophobic layer is formed in the cavity C throughthe injection hole H (FIGS. 1 and 3), a thickness of the hydrophobiclayer in the cavity C may become non-uniform. The thickness of thehydrophobic layer in the vicinity of the injection hole H in the cavityC may be greater than the thickness of the hydrophobic layer formed onthe center portion of the cavity C which is remote from the injectionhole H. However, since the hydrophobic layer 130 according to theexample is formed of the self-assembled monolayer 131, the thickness ofthe hydrophobic layer is uniform regardless of the position in thecavity C.

Since the hydrophobic layer 130 is formed after a first metal layer 180and a second metal layer 190 are formed as described below, thehydrophobic layer 130 may be formed on the protective layer 127 otherthan portions on which the first metal layer 180 and the second metallayer 190 are formed.

Further, the hydrophobic layer 130 may also be disposed on an uppersurface of the cavity C, other than the protective layer. As describedbelow, the hydrophobic layer may be formed on the upper surface of thecavity simultaneously with the hydrophobic layer on the protective layerin the operation of forming the hydrophobic layer on the protectivelayer, and the hydrophobic layer in the cavity C may be formed on atleast a portion of a lower surface and a side surface of the cavity C aswell as on the upper surface of the cavity C.

Since the resonating portion 120 is disposed on the cavity C, the uppersurface of the cavity C may also affect the change in the frequency ofthe acoustic resonator. Therefore, in a case in which the hydrophobiclayer is formed on the upper surface of the cavity C, the change in thefrequency of the acoustic resonator may be significantly reduced.

Filter

FIG. 14 is a schematic circuit diagram of a first example of a filter.FIG. 15 is a schematic circuit diagram of a second example of a filter.

Each of a plurality of bulk acoustic resonators employed in the filtersof FIGS. 14 and 15 may correspond to the first example of an acousticresonator illustrated in FIGS. 1-4 and described above, as well as, asecond example of an acoustic resonator illustrated in FIGS. 9 and 10.

Referring to FIG. 14, a filter 1000 according to the first example of afilter is formed in a ladder type filter structure. Specifically, thefilter 1000 includes a first acoustic resonator 1100 and a secondacoustic resonator 1200.

A first acoustic resonator 1100 is connected in series between a signalinput terminal to which an input signal RFin is input and a signaloutput terminal from which an output signal RFout is output, and asecond acoustic resonator 1200 is connected between the signal outputterminal and a ground.

Referring to FIG. 15, a filter 2000 according to the second example of afilter is formed in a filter structure of a lattice type. Specifically,the filter 2000 includes a third acoustic resonator 2100, a fourthacoustic resonator 2200, a fifth acoustic resonator 2300, and a sixthacoustic resonator 2400 to filter balanced input signals RFin+ and RFin−and to output balanced output signals RFout+ and RFout−.

Further, a third example of a filter may be formed in a filter structurein which the filter structure of the ladder type of FIG. 14 and thefilter structure of the lattice type of FIG. 15 are combined.

Method for Manufacturing Acoustic Resonator

Next, an example method for manufacturing an acoustic resonator will bedescribed.

FIGS. 5 through 8 are views illustrating an example method formanufacturing an acoustic resonator.

Referring to FIG. 5, in the example method for manufacturing theacoustic resonator, the insulating layer 115 and the sacrificial layer140 are formed on the substrate 110, and a pattern P penetrating throughthe sacrificial layer 140 is formed. Therefore, the insulating layer 115is exposed to the outside through the pattern P.

The insulating layer 115 may be formed of magnesium oxide (MgO),zirconium oxide (ZrO₂), aluminum nitride (AlN), lead zirconate titanate(PZT), gallium arsenic (GaAs), hafnium oxide (HfO₂), aluminum oxide(Al₂O₃), titanium oxide (TiO₂), zinc oxide (ZnO), silicon nitride(Si₃N₄), silicon dioxide (SiO₂), or the like, but are not limitedthereto.

The pattern P formed in the sacrificial layer 140 may have a crosssection of a trapezoidal shape in which a width of an upper surface isgreater than a width of a lower surface.

The sacrificial layer 140 is partially removed by a subsequent etchingprocess to form the cavity C (FIG. 2). Therefore, the sacrificial layer140 may be formed of a material such as polysilicon, polymer, or thelike which may be easily etched. However, the material of thesacrificial layer 140 is not limited thereto.

The membrane layer 150 is formed on the sacrificial layer 140. Themembrane layer 150 may have a constant thickness along a surface of thesacrificial layer 140. The thickness of the membrane layer 150 may bethinner than that of the sacrificial layer 140.

The membrane layer 150 may include at least one of silicon dioxide(SiO₂) and silicon nitride (Si₃N₄). Further, the membrane layer 150 maybe formed of a dielectric layer containing at least one of magnesiumoxide (MgO), zirconium oxide (ZrO₂), aluminum nitride (AlN), leadzirconate titanate (PZT), gallium arsenide (GaAs), hafnium oxide (HfO₂),aluminum oxide (Al₂O₃), titanium oxide (TiO₂), and zinc oxide (ZnO), ora metal layer containing at least one of aluminum (Al), nickel (Ni),chromium (Cr), platinum (Pt), gallium (Ga), and hafnium (Hf). However,the configuration of the present disclosure is not limited thereto.

A seed layer (not shown) may be formed on the membrane layer 150.

The seed layer may be disposed between the membrane layer 150 and thefirst electrode 121. The seed layer may be manufactured of aluminumnitride (AlN), but is not limited thereto, and may also be formed of adielectric or a metal having an HCP structure. For example, in a case inwhich the seed layer is formed of a metal, the seed layer may be formedof titanium (Ti).

As illustrated in FIG. 6, the etching stop layer 145 a is formed on themembrane layer 150. The etching stop layer 145 a is also filled in thepattern P.

The etching stop layer 145 a may have a thickness that completely fillsthe pattern P. Therefore, the etching stop layer 145 a may have agreater thickness than the sacrificial layer 140.

The etching stop layer 145 a may be formed of the same material as theinsulating layer 115, but is not limited thereto.

The etching stop layer 145 a is removed so that the membrane layer 150is exposed to the outside.

Here, the portion of the etching stop layer 145 a filled in the patternP is left, and the left etching stop layer 145 a serves as the etchingstop part 145.

As illustrated in FIG. 7, the first electrode 121 is formed on themembrane layer 150.

The first electrode 121 is formed of a conductor, and may be formed of,for example, gold, molybdenum, ruthenium, iridium, aluminum, platinum,titanium, tungsten, palladium, tantalum, silver, copper, chromium,nickel, or a metal including at least one thereof, but is not limitedthereto.

The first electrode 121 is formed on a region in which the cavity C(FIG. 3) is formed.

The first electrode 121 may be formed by forming a conductor layer onthe entirety of the membrane layer 150 and then removing an unnecessaryportion.

The insertion layer 170 may be formed as needed. The insertion layer 170is formed on the first electrode 121 and may be extended upwardly fromthe membrane layer 150 as needed. When the insertion layer 170 isformed, since the extending portion E of the resonating portion 120 hasa greater thickness than the center portion S, Q-factor of the acousticresonator 100 may be increased by suppressing vibration generated at thecenter portion S from escaping to the extending portion E.

The insertion layer 170 may be disposed by covering the entirety of thesurface formed by the membrane layer 150, the first electrode 121, andthe etching stop layer 145 and removing a portion disposed on a regioncorresponding to the center portion S.

Accordingly, a central portion of the first electrode 121 configuringthe center portion S is exposed to the outside of the insertion layer170. Further, the insertion layer 170 covers a portion of the firstelectrode 121 along a perimeter of the first electrode 121. Therefore,an edge portion of the first electrode 121 disposed on the extendingportion E may be disposed below the insertion layer 170.

A side surface of the insertion layer 170 disposed to be adjacent to thecenter portion S is formed as an inclined surface L. The insertion layer170 is thinner toward the center portion S, and accordingly, the lowersurface of the insertion layer 170 extends further toward the centerportion S than an upper surface of the insertion layer 170. Here, theinclined angle of the inclined surface L of the insertion layer 170 isin the range of about 5° to about 70°, as described above.

The insertion layer 170 may be formed of, for example, a dielectric suchas silicon dioxide (SiO₂), aluminum nitride (AlN), aluminum oxide(Al₂O₃), silicon nitride (Si₃N₄), magnesium oxide (MgO), zirconium oxide(ZrO₂), lead zirconate titanate (PZT), gallium arsenide (GaAs), hafniumoxide (HfO₂), aluminum oxide (Al₂O₃), titanium oxide (TiO₂), zinc oxide(ZnO), or the like, but may be formed of a material different from thepiezoelectric layer 123.

The piezoelectric layer 123 is formed on the first electrode 121 and theinsertion layer 170.

The piezoelectric layer 123 may be formed of aluminum nitride (AlN).However, the piezoelectric layer 123 is not limited thereto and as amaterial of the piezoelectric layer 123, zinc oxide (ZnO), dopedaluminum nitride, lead zirconate titanate, quartz, and the like may beselectively used. Further, the doped aluminum nitride may furtherinclude a rare earth metal or a transition metal. As an example, therare earth metal may include at least one of scandium (Sc), erbium (Er),yttrium (Y), cerium (Ce), and lanthanum (La). The transition metal mayinclude at least one of hafnium (Hf), titanium (Ti), zirconium (Zr),tantalum (Ta), niobium (Nb), and magnesium (Mg).

Further, the piezoelectric layer 123 may be formed of a same material asthe insertion layer 170 or a material different from the insertion layer170.

The piezoelectric layer 123 may be disposed by forming a piezoelectricmaterial on the entirety of the surface formed by the first electrode121 and the insertion layer 170 and then partially removing anunnecessary portion. The piezoelectric layer 123 may be completed byforming the second electrode 125 and then removing an unnecessaryportion of the piezoelectric material. However, forming thepiezoelectric layer 123 is not limited thereto, but may alternatively becompleted before the second electrode 125 is formed.

The piezoelectric layer 123 partially covers the first electrode 121 andthe insertion layer 170, and accordingly, the piezoelectric layer 123 isformed along an edge of the surface formed by the first electrode 121and the insertion layer 170.

As described above, only a portion of the first electrode 121corresponding to the center portion S may be exposed to the outside ofthe insertion layer 170. Therefore, the piezoelectric layer 123 formedon the first electrode 121 may be disposed in the center portion S. Inaddition, the bending portion 123 b formed on the insertion layer 170 isdisposed in the extending portion E.

The second electrode 125 is formed on the piezoelectric layer 123. Thesecond electrode 125 is formed of a conductor, and may be formed of, forexample, gold, molybdenum, ruthenium, iridium, aluminum, platinum,titanium, tungsten, palladium, tantalum, silver, copper, chromium,nickel, or a metal including at least one thereof, but is not limitedthereto.

The second electrode 125 may be basically formed on the piezoelectricportion 123 a of the piezoelectric layer 123. As described above, thepiezoelectric portion 123 a of the piezoelectric layer 123 is disposedin the center portion S. Therefore, the second electrode 125 disposed onthe piezoelectric layer 123 is also disposed in the center portion S.

Further, the second electrode 125 is also formed on the inclined portion1231 of the piezoelectric layer 123. Accordingly, as described above,the second electrode 125 is disposed in the center portion S and theextending portion E. The second electrode 125 may be partially disposedin the extending portion E, thereby providing remarkably improvedresonance attenuation.

As illustrated in FIG. 8, the protective layer 127 is formed.

The protective layer 127 is formed along a surface formed by the secondelectrode 125 and the piezoelectric layer 123. Further, although notillustrated, the protective layer 127 may also be formed on theinsertion layer 170 which is exposed to the outside.

The protective layer 127 is formed of an insulating material such assilicon oxide based insulating material, silicon nitride basedinsulating material, and aluminum nitride based insulating material, butis not limited thereto.

The first electrode 121 and the second electrode 125 are partiallyexposed by partially removing the protective layer 127 and thepiezoelectric layer 123, and the first metal layer 180 and the secondmetal layer 190 are each formed on the exposed portions. That is, thefirst metal layer 180 is formed on the exposed portion of the firstelectrode 121 and the second metal layer 190 is formed on the exposedportion of the second electrode 125.

The first metal layer 180 and the second metal layer 190 may be formedof materials such as gold (Au), a gold-tin (Au—Sn) alloy, copper (Cu), acopper-tin (Cu—Sn) alloy, and the like, and may be formed to bedeposited on the first electrode 121 or the second electrode 125, butare not limited thereto.

The cavity C is formed by removing a portion of the sacrificial layer140 disposed in the etching stop part 145, and the sacrificial layer 140removed during this process may be removed by an etching manner.

In a case in which the sacrificial layer 140 is formed of a materialsuch as polysilicon, polymer, or the like, the sacrificial layer 140 maybe removed by a dry etching method using a halide-based etching gas (forexample, XeF₂) such as fluorine (F), chlorine (Cl), and the like.

A trimming process using a wet process is performed to obtain desiredfrequency characteristics.

Manufacturing of the first example acoustic resonator 100 illustrated inFIGS. 1-4 and the second example acoustic resonator 100 illustrated inFIGS. 9 and 10, includes forming the hydrophobic layer 130 on theprotective layer 127.

The hydrophobic layer 130 is formed by depositing a hydrophobic materialby a chemical vapor deposition (CVD) method.

For example, hydroxylate may be formed on a surface of the protectivelayer 127 formed of SiO₂ as illustrated in FIG. 17. The surface of theprotective layer 127 may be surface-treated by performing a silanehydrolysis reaction for such hydroxylate using a precursor having asilicon head.

Thereafter, the hydrophobic layer 130 may be formed on the protectivelayer 127 as illustrated in FIG. 19 by forming a fluorocarbon functionalgroup on the surface-treated surface of the protective layer.

Alternatively, the hydrophobic layer 130 may be formed by omitting thesurface treatment depending on the material of the protective layer, andforming the fluorocarbon functional group on the protective layer 127.

In the operation of forming the hydrophobic layer described above, thehydrophobic layer may also be formed on the upper surface of the cavityC through the injection hole H (FIGS. 1 and 3), the hydrophobic layermay also be formed on at least a portion of a lower surface and a sidesurface of the cavity C as well as the upper surface of the cavity C,and the hydrophobic layer may also be formed on the entirety of theupper, lower, and side surfaces of the cavity C.

Further, the hydrophobic layer 130 is formed of the self-assembledmonolayer 131, not the polymer, thereby preventing mass loading due tothe hydrophobic layer 130 from being applied to the resonating portion120. The hydrophobic layer 130 formed of the self-assembled monolayer131 provides a uniform thickness of the hydrophobic layer 130.

According to the examples described above, a hydrophobic layer isdisposed on a protective layer, whereby frequency fluctuation may besignificantly reduced and performance of a resonator may be uniformlymaintained even when the acoustic resonator is used in a humidenvironment or left at room temperature for a long time.

While this disclosure includes specific examples, it will be apparentafter an understanding of the disclosure of this application thatvarious changes in form and details may be made in these exampleswithout departing from the spirit and scope of the claims and theirequivalents. The examples described herein are to be considered in adescriptive sense only, and not for purposes of limitation. Descriptionsof features or aspects in each example are to be considered as beingapplicable to similar features or aspects in other examples. Suitableresults may be achieved if the described techniques are performed in adifferent order, and/or if components in a described system,architecture, device, or circuit are combined in a different manner,and/or replaced or supplemented by other components or theirequivalents. Therefore, the scope of the disclosure is defined not bythe detailed description, but by the claims and their equivalents, andall variations within the scope of the claims and their equivalents areto be construed as being included in the disclosure.

What is claimed is:
 1. An acoustic resonator comprising: a membranelayer disposed on an insulating layer; a cavity formed by the insulatinglayer and the membrane layer; a resonating portion disposed on thecavity and comprising a first electrode, a piezoelectric layer, and asecond electrode stacked thereon; a protective layer disposed on theresonating portion; and a hydrophobic layer disposed on the protectivelayer, wherein the protective layer is disposed between the hydrophobiclayer and the second electrode.
 2. The acoustic resonator of claim 1,wherein the hydrophobic layer is further disposed on an upper surface ofthe cavity.
 3. The acoustic resonator of claim 2, wherein thehydrophobic layer is further disposed on at least a portion of a lowersurface and a side surface of the cavity.
 4. The acoustic resonator ofclaim 1, wherein the hydrophobic layer is a self-assembled monolayer. 5.The acoustic resonator of claim 1, wherein the hydrophobic layercomprises a fluorine (F) component.
 6. The acoustic resonator of claim5, wherein the hydrophobic layer further comprises a silicon (Si)component.
 7. The acoustic resonator of claim 1, wherein the resonatingportion comprises a center portion, and an extending portion extendingoutward from the center portion and in which an insertion layer isdisposed below the piezoelectric layer, and wherein the piezoelectriclayer comprises a piezoelectric portion disposed in the center portion,and a bending portion disposed in the extending portion and extendinginclined from the piezoelectric portion along an edge of the insertionlayer.
 8. The acoustic resonator of claim 1, further comprising aninsertion layer disposed below the piezoelectric layer, wherein theinsertion layer comprises an inclined surface having a thickness thatincreases as a distance from a center portion of the piezoelectric layerincreases.